... in the trachea. The cause of abrupt jumps in frequency has not been identified but can be explained on the basis of intrinsic properties of the vocal organ. Air sac pressure variation as a mechanism for frequency modulation contrasts with the specialized syringeal musculature of songbirds and may explain why...

... of Biologists Limited 1998 diving air sac avian respiratory system air sac pressure tufted duck Aythya fuligula There is evidence that aerobic metabolism is the major source of energy production during normal feeding dives in many aquatic birds ( Butler and Jones, 1997 ). To accommodate...